Treating rubber to enhance fiber bonding

ABSTRACT

Fiber to rubber adhesion is enhanced by incorporating into the rubber a formaldehyde donor and a saturated polymer comprising alkylene bridged resorcinol.

States Patent finite Morita 5] Feb.22,1972

' 221 Filed:

[54] TREATING RUBBER TO ENHANCE FIBER BONDING [52] US. Cl. ..260/38,260/3, 260/415 A,

260/845 [51] Int. Cl. ..C08d 9/10 [58] Field of Search ..260/38,4l.5 R,3, 845,415 A [56] References Cited UNITED STATES PATENTS 3,408,24910/1968 Broma ..260/3X 3,528,473 9/1970 Tortietal.....

OTHER PUBLICATIONS New Adhesive System Saves Time, Money, Chemical andEngineering News, Apr. 22, 1968 p. 40- l.

Primary ExaminerMorris Liebman Assistant Examiner-S. M. PersonAtt0rneyRichard O. Zerbe, J. E. Maurer and Neal E. Willis ABSTRACT Fiberto rubber adhesion is enhanced by incorporating into the rubber aformaldehyde donor and a saturated polymer comprising alkylene bridgedresorcinol.

7 Claims, No Drawings TREATING RUBBER TO ENHANCE FIBER BONDING Thisinvention relates to methods of treating rubber to enhance the bondingto fiber reinforcing elements and to the rubber products so obtained.

BACKGROUND OF THE INVENTION The addition to rubber of silica, resorcinoland hexamethylenetetramine or other formaldehyde donor yields rubbercompositions having increased affinity for fiber reinforcing elements.The treatment of rubber instead of the fiber for preparing fiber torubber bonded composites has a number of advantages and this inventionis concerned with improvements in treating the rubber component althoughit may be practiced in conjunction with treated fiber if desired andfurther improvements may sometimes be obtained thereby.

SUMMARY OF THE INVENTION Adhesion of fiber to rubber is promoted byincorporating into the rubber a formaldehyde donor and an essentiallysaturated polymer of resorcinol and an unsaturate. The presence of thesaid polymer in the rubber also promotes building tack. The polymerscontain alkylene diresorcinol units comprising alkylene bridgedresorcinol oftwo or more resorcinol units.

The unsaturate-resorcinol polymers characterized by resorcinol units maybe produced by the acidic condensation of resorcinol with an unsaturate.The alkylene bridge may be derived from an unsaturate selected from thegroup consisting of 1) a halo-olefin of three to carbon atoms, (2) adihaloolefin of three to 10 carbon atoms, (3) an acyclic or cyclicdiolefin of three to 10 carbon atoms or (4) an alkine of two to 10carbon atoms. Acidic conditions favor introduction of an unsaturatedgroup into the resorcinol nucleus and further condensation occurs untilessentially no unsaturation remains.

Generally, the reaction may be effected between 50 and 150 C. preferablyby adding the unsaturate under acidic conditions to resorcinol. Highertemperatures are preferred because the reaction is completed in ashorter time. The reaction may be carried out by adding the unsaturateto molten resorcinol, but it is generally more convenient to conduct thereaction with the resorcinol in an inert solvent. The use of a solventaids in mixing the reactants, provides a uniform reaction temperatureand permits easy removal of byproducts. A number of solvents aresuitable reaction media; the only requisites are that the solvent doesnot react with any of the starting materials or products of the reactionand is easily removed from the final product. Xylene is an excellentsolvent for this purpose.

The mole ratio of unsaturate to resorcinol is 0.5 to 2.0 moles per moleof resorcinol. The unsaturate is either an alkine or olefin having twoor more reactive sites, one of which is an ethylenically unsaturatedbond. More specifically, a straight, branched chain, or cyclic diolefinmay be used, or a monoor dihalo-olefin. When using an unsaturate havingno halogen present such as an alkine or diolefin hydrocarbon, it isnecessary to add a sufficient quantity of an acid, such as hydrogenchloride, to assure that the reaction is conducted under acidicconditions. When using the halo-olefins, no additional acid is requiredsince hydrogen halide is a byproduct which maintains acidic conditionsin the reaction mixture. An olefin of three to 10 carbon atoms ispreferred. The addition of other catalysts is not necessary but may beused if desired. Examples of other catalysts are sulfuric acid, acidclay, zinc chloride and cuprous chloride. In the presence of cuprouschloride alkenyl resorcinols form under mild reaction conditions andheating in the presence of resorcinol easily affects an exothermicreaction resulting in formation of the adhesive.

Halo-olefins suitable for the practice of this invention are illustratedby 3-chloropropene, 3-chloro-l-butene, 4-chloro-ibutene,l-cbloro-2-butene, 3-chloro-2-methylpropene, 3- chloro-l-pentene,5-chloro-2-pentene, 4-chloro-2-methyl-2- butene, 4-chloro-1-hexene,6-chloro-l-hexene, 2-chloro-3- hexene, l-chloro-3-hexene and their halocounterparts in place of chlorine.

DESCRIPTION OF PREFERRED EMBODIMENTS A solution of 220 grams (two moles)of resorcinol in 400 ml. of xylene is prepared and heated to 100-l20 C.Allyl chloride is then added and after the reaction is complete theupper solvent layer is decanted and the residual solvent is removed byheating the remaining reaction mixture in vacuo. A summary of threepreparations in which the ally] chloride varied is as follows:

Allyl Total Wt. of Reaction Chloride Feed Time Heating Time Product,grams 1 mole 85 min. 4 hr. 200 2 moles 3 hr. 55 hr. 256 3 moles 5 hr.8.5 hr. 299

The apparent molecular weight distribution analyzed by gel me shrematqspbxis mm r e below:

Percent apparent MW 180 232 456 675 Average Allyl chloride:

1 mole 2 40 26 17 15 (1,000) 3 2s 19 16 34 1,200) 4 15 A rubber stock iscompounded comprising:

Base Stock Parts by weight Smoked sheet rubber 50 Styrene butadienecopolymer rubber 68.8 Furnace carbon black (FEF) 35 Silica (Hi Sil 233)15 .Zinc oxide 3 Stearic acid 2 N-cyclohexyl-Z-benzothiazolesulfenamidel 'Hexamethylenetetramine 1.6 Sulfur 2.0

The relative adhesion characteristics between fiber and vulcanizedrubber product are determined by measuring the force required to pull atreated cord embedded in a strip of vulcanized rubber prepared from theforegoing base stock. The test is called an H-test and derives its namefrom the ,shape of the rubber cord article formed in the vulcanizationmold. To the base stock is added 2.5 parts of resorcinol or 2.5 parts ofthe saturated alkylene diresorcinol polymer prepared .from allylchloride and resorcinol in the ratio indicated in the 4 table below. Thebase stock alone serves as control. Polyester cord is embedded in therubber and is cured in the conventional I-I-test sample mold havingrubber strip channels threeeighths inch wide by 0.1 inch deep andseparated from one another by one-fourth inch. In one series of teststhe cord embedded in the rubber is untreated. In the second series oftests the cord is coated or dipped in a solution of the same material asadded to the base stock. Thus, the cord is treated with allyl H-TestAdhesion to Polyester (lb.) Addition to Base Stock Untreated TreatedNone 3.] Resorcinol 2.9 12.1 Allyl chloride OAS/resorcinol 1.0 9.7 14.5Allyl chloride 1.0/resorcinol 1.0 12.3 12.8 Allyl chlorideZ.(l/resorcinol L 3.6 8.6

Cords treated with other treating agents, for example RFL,

give improved adhesion values when the polymers of this invention areadded to the rubber stock.

The adhesion of rayon and nylon to the stocks containing the allylchloride resorcinol reaction product as compared to the base stock aloneis shown by the following.

H-Test Adhesion of Untreated Cord (1b.) Addlllfln in Bust: Stuck RayonNylon None 6.7 3.3 I Allyl chloride Old/resorcinol l.0 24.0 123 Ailylchloride 1.0/resorcinol L0 251 22.1 Allyl chloride 2.0/resorcinol [.07.8 4.2

Although it is preferable for obtaining maximum adhesion for the stocksto contain silica, the invention is not limited thereto since cord torubber adhesion is improved in the absence of silica. A rubber stock isprepared similar to the previously described recipe except additionalparts carbon black are used in place of the silica. The otheringredients are the same except for hexamethylenetetramine, which isadded in the indicated amounts as shown below.

The unsaturate-resorcinol polymers are good tackifiers for syntheticelastomers. Natural rubber has sufficient tack to enable fabrication ofproducts without layer separation before vulcanization. However, manysynthetic elastomers are so P deficient in tack that products cannot befabricated without using tackifiers to enhance the adhesion of thecomponents.

The tackifying property of the instant polymers is illustrated bycomparing the tack ofa styrene-butadiene copolymer stock with the tackof the same stock containing the unsaturateresorcinol polymer. The tackproperties are determined by means ofa Skewis tackmeter by the methoddescribed by J. D. Skewis, Rubber Chem. Technol. 38, 689 (1965). Thevalues obtained are the time in seconds which is required to separatetwo specimens of the test material. Longer times are indicative ofimproved cohesion. The values shown below are the average of fivedeterminations. Sample A comprises 100 parts (all parts by weight)styrene-butadiene copolymer, 52 parts HAF carbon black and 10 parts higharomatic processing oil. Sample B comprises, in addition to the sameingredients as in Sample A, 5 parts of allyl chloride 1.0/resorcinol 1.0reaction product.

Sample Tack (see) A 44 B I I2 The adhesives of this invention may beused with natural rubber, synthetic rubber having sufficient unsaturation to enable sulfur vulcanization, or mixtures thereof. Examples ofsuitable synthetic rubbers are styrene-butadiene copolymer,isobutylene-isoprene copolymer, ethylene-propylene-diene terpolymers,butadiene-acrylonitrile copolymer, polymers of chloroprene and syntheticpolyisoprene. The polymers of this invention may be advantageously usedin rubber stocks containing the commonly used accelerators,antidegradants, fillers and reinforcement agents. The amount of polymerrequired depends upon a number of factors but generally falls within therange of 0.5-10.0 parts per lOO parts elastomer.

Any formaldehyde donor which upon heating releases formaldehyde orfurnishes radicals capable of forming methylene bridges is suitable forthe practice of this invention. Examples of such materials arehexamethylenetetramine, hexamethoxymethylmelamine,cyclotrimethyltriamines and [(hydroxymethyl)ethylidene1alkylamines.

Other fibers than those particularly mentioned may be incorporated intorubber stocks prepared according to this invention. Examples are fibersof cotton, wool, wood cellulose, glass, aluminum, copper, tin, steel,brass plated steel and aluminum-steel alloys. The preparation ofaluminum-steel alloy fibers and stainless steel fibers useful for makingreinforced rubber articles is described in British Patent No. 1,153,577,May 29, 1969. Although the invention has been illustrated by typicalexamples, it is not limited thereto. Changes and modifications of theexamples of the invention herein chosen for purposes of disclosure canbe made which do not constitute departure from the spirit and scope ofthe invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. The method of making a rubber stock having enhanced adhesion to fiberwhich comprises incorporating therein a formaldehyde donor and acomposition consisting essentially of an adhesion-enhancing amount of anessentially saturated polymer of resorcinol and an unsaturate selectedfrom the group consisting of (l) halo-olefin of three to 10 carbonatoms, (2) dihalo-olefin of three to lO carbon atoms, (3) acyclic orcyclic diolefin of three to 10 carbon atoms and (4) alkine of two to 10carbon atoms said polymer comprising alkylene diresorcinol units.

2. The method of claim 1 where the polymer is prepared by reaction of0.5 to 2 moles of unsaturate per mole of resorcinol.

3. The method of claim 1 where the polymer is the composite reactionproduct of about 0.5 to about 1 mole of allyl chloride per mole ofresorcinol.

4. The method of claim 1 comprising the additional step of adding silicato the rubber stock.

5. The method of claim 1 comprising the additional step of incorporatingpolyester fiber into the rubber stock.

6. The method of claim 2 wherein the unsaturate is allyl chloride.

7. The method of claim 3 comprising the additional step of incorporatingpolyester fiber into the rubber stock which fiber is treated with thesaid polymer which is the composite reaction product of about 0.5 toabout 1 mole of allyl chloride per mole of resorcinol.

2. The method of claim 1 where the polymer is prepared by reaction of0.5 to 2 moles of unsaturate per mole Of resorcinol.
 3. The method ofclaim 1 where the polymer is the composite reaction product of about 0.5to about 1 mole of allyl chloride per mole of resorcinol.
 4. The methodof claim 1 comprising the additional step of adding silica to the rubberstock.
 5. The method of claim 1 comprising the additional step ofincorporating polyester fiber into the rubber stock.
 6. The method ofclaim 2 wherein the unsaturate is allyl chloride.
 7. The method of claim3 comprising the additional step of incorporating polyester fiber intothe rubber stock which fiber is treated with the said polymer which isthe composite reaction product of about 0.5 to about 1 mole of allylchloride per mole of resorcinol.